Adaptive, return electrode monitoring system

Abstract

A return electrode monitoring system for use with a split patient return electrode having two, electrically isolated electrode elements adapted for contacting a patient, the system comprising means responsive to the impedance between the two electrode elements for producing a signal which is a function of the impedance; means for establishing a desired range having an upper limit and a lower limit for the impedance when the patient is in contact with the electrode elements; determining means responsive to the signal for determining whether the impedance is within the desired range; and adjusting means for adjusting the upper limit to adapt the system to the particular impedance of the patient in response to the particular impedance occurring within the desired range.

We claim: 
     
       1. A return electrode monitoring system for use with a split patient return electrode having two, electrically isolated electrode elements adapted for contacting a patient, said system comprising means responsive to the impedance between said two electrode elements for producing a signal which is a function of said impedance;   means for establishing a desired range having an upper limit and a lower limit for said impedance when the patient is in contact with the electrode elements;   determining means responsive to said signal for determining whether said impedance is within said desired range; and   adjusting means for automatically adjusting said upper limit to adapt said system to the particular impedance of said patient in response to said particular impedance occurring within the desired range.   
     
     
       2. A system as in claim 1 including means for respectively presetting said upper and lower limits to 120 and 20 ohms. 
     
     
       3. A system as in claim 1 where said adjusting means includes means for adjusting the upper limit to a value greater than the said patient's particular impedance by a predetermined percentage of the particular impedance. 
     
     
       4. A system as in claim 3 where said predetermined percentage is 120%. 
     
     
       5. A system as in claim 1 or 3 including delay means for delaying the operation of said adjusting means until a predetermined amount of time has elapsed from the first occurrence of the patient's particular impedance within the desired range. 
     
     
       6. A system as in claim 5 where said predetermined amount of time is 5 seconds. 
     
     
       7. A system as in claim 1 or 3 including means for detecting a change in the patient's particular impedance to a decreased value and where said adjusting means includes decreasing means for decreasing the upper limit of the desired range to a value related to said decreased value. 
     
     
       8. A system as in claim 7 where said decreasing means includes means for decreasing the upper limit to a value greater than the decreased value of the patient's particular impedance by a predetermined percentage of the decreased value. 
     
     
       9. A system as in claim 8 where said predetermined percentage is 120%. 
     
     
       10. A system as in claim 7 including delay means for delaying the operation of said adjusting means until a predetermined amount of time has elapsed from the occurrence of said decreased value of the patient's particular impedance. 
     
     
       11. A system as in claim 10 where said predetermined amount of time is 5 seconds. 
     
     
       12. A system as in claim 1 including transition detection means for detecting a transition of said patient's particular impedance from within the desired range to outside the range and changing means for changing the one of said upper and lower limits in response to said transition. 
     
     
       13. A system as in claim 12 where said transition detection means includes means for detecting said transition of the patient's particular impedance to a value greater than the upper limit and where said changing means includes means for decreasing the upper limit in response to said transition. 
     
     
       14. A system as in claim 13 where said means for decreasing the upper limit includes means for decreasing the uppr limit from 120% of the patient's particular impedance to 115% of the patient's particular impedance. 
     
     
       15. A system as in claim 12 or 13 where said transition detection means includes means for detecting said transition of the patient's particular impedance to a value less than the lower limit and where said changing means includes means for increasing the lower limit in response to said transition. 
     
     
       16. A system as in claim 15 where said means for increasing the lower limit includes means for increasing the lower limit from 20 to 24 ohms. 
     
     
       17. A system as in claim 1 including means for presetting said upper limit to an initial value; means for detecting a transition of said patient's particular impedance from within the desired range to a value greater than the upper limit; timing means for establishing a predetermined time interval after the occurrence of said transition; and means for resetting the upper limit to said initial value if the patient's particular impedance remains in excess of a maximum amount for said pre-determined time interval. 
     
     
       18. A system as in claim 17 where said predetermined time interval is one second. 
     
     
       19. A system as in claim 1, 3 or 17 including means for detecting the transition of said patient's particular impedance from within the desired range to outside the range and means for disabling the system in response to the occurrence of the transition. 
     
     
       20. A system as in claim 1, 3 or 17 including means for detecting the transition of said patient's particular impedance from within the desired range to outside the range and means for generating an alarm signal in response to the occurrence of the transition. 
     
     
       21. A return electrode monitoring system for use with a common foil, patient return electrode adapted for contacting a patient, said electrode having two, spaced apart conductors attached thereto for connecting the electrode to a generator of electrosurgical current, said system comprising microprocessor means for monitoring the continuity of the circuit including said electrode, said conductors, and said generator including means responsive to the impedance between said two conductors for producing a signal which is a function of said impedance;   means for establishing a desired upper limit for said impedance;   determining means responsive to said signal for determining whether said impedance is below said desired upper limit; and     transition detecting means for detecting a transition of said impedance from a value less than said upper limit to a value greater than said upper limit and means for decreasing the value of the upper limit to a lower value in response to said transition.   
     
     
       22. A system as in claim 21 where said means for establishing a desired upper limit includes means for generating a reference signal corresponding to the upper limit and where said determining means includes comparator means for comparing the signal which is a function of said impedance with the reference signal. 
     
     
       23. A return electrode as in claim 21 where said desired upper limit is 20 ohms. 
     
     
       24. A system as in claim 21 including means for disabling the system in response to the occurrence of the transition. 
     
     
       25. A system as in claim 21 including means for generating an alarm signal in response to the occurrence of the transition. 
     
     
       26. A system as in claim 21 where said desired upper limit is 20 ohms and said lower value is 16 ohms.